1. Field of the invention
The present invention relates to an electric power steering apparatus using a motor as a generation source of steering assistance force.
2. Description of Related Art
FIG. 1 is a front view showing a constitution of a conventional electric power steering apparatus.
As shown in FIG. 1, for example, an electric power steering apparatus for a vehicle comprises: a steering shaft 101 joined to a steering wheel 100 for steering; a shaft housing 102 for accommodating said steering shaft 101; a steering assist motor 104 for assisting operation of a steering mechanism joined via a joint to the steering shaft 101, the steering assist motor 104 having a rotor arranged so that a rotational center thereof intersects an axis of the steering shaft 101 and a cylindrical motor housing 103 for supporting said rotor; fastening members 105 for supporting one end portion of the motor housing 103 on a lower end portion of the shaft housing 102; a lower mounting member 106 for mounting a lower end portion of the shaft housing 102 to a car body (see FIG. 2); and an upper mounting member 108 for mounting an axially middle portion of the shaft housing 102 to the car body 109, the upper mounting member 108 having an impact energy absorber 107 for absorbing impact energy of a secondary crash.
The steering shaft 101 is divided into an upper shaft 101a joined to the steering wheel 100 and a lower shaft 101b joined to the joint, the divided end portions being connected to each other by an impact energy absorber for absorbing impact energy of a secondary crash. The shaft housing 102 is divided into an upper shaft housing 102a to which the upper mounting member 108 is mounted and a lower shaft housing 102b to which the motor 104 and the lower mounting member 106 are mounted, the divided end portions being engaged with each other so as to be movable relatively.
FIG. 2 is a schematic representation showing a state of a conventional electric power steering apparatus mounted to a car body.
The electric power steering apparatus constituted as above is disposed in a passenger's room. As shown in FIG. 2, the lower mounting member 106 and the upper mounting member 108 are mounted to the car body 109. The joint 110, which connects the steering shaft 101 and the steering mechanism of the electric power steering apparatus mounted to the car body 109, is disposed through an instrument panel 111 of the car body 109.
When a vehicle having an electric power steering apparatus mounted thereto as above makes a crash, such as a frontal crash, the instrument panel 111 of the car body 109 is occasionally transformed toward the interior of the passenger's room by the crash (a primary crash). When a driver crashes (a secondary crash) into the steering wheel 100 by the action of a shock of a primary crash, impact energy is applied to the upper steering shaft 101a, and further to the upper shaft housing 102a via said upper steering shaft 101a. Since the upper steering shaft 101a and the upper shaft housing 102a are pressured in an axial direction in this case, the impact energy absorber of the steering shaft 101 and the impact energy absorber 107 of the upper mounting member 108 are destroyed, and the upper steering shaft 101a and the upper shaft housing 102a move relatively with the lower steering shaft 101b and the lower shaft housing 102b. The impact energy of the secondary crash can thus be absorbed.
However, the steering assist motor 104 of the electric power steering apparatus which is constituted as the above projects outward in a radial direction of the shaft housing 102 on a relatively large scale. Moreover, said motor 104 is fixed to the lower shaft housing 102b with fastening members 105. At the time of the secondary crash, a driver's leg occasionally strikes against the motor 104 since the upper shaft housing 102a moves relatively with the upper shaft housing 102b to which the motor 104 is mounted. Consequently, there arises a problem in that driver's damage becomes serious. Moreover, when the instrument panel 111 or the like of the car body 109 strikes against the motor 104 at the time of the primary crash, transformation of the instrument panel 111 or the like is hindered by the motor 104, thereby preventing absorption of impact energy.